PROJECT SUMMARY. Existing treatments for pulmonary fibrosis have not significantly improved survival; there is a critical need for new approaches. A combination of environmental and genetic factors creates an alveolar epithelium that is susceptible to injury. Deregulated repair of damaged tissue leads to the hyperplastic and proliferating alveolar type II cells (AECII) ? the so called ?re-programmed? AECII, which are main pathological features in the lungs of patients with fibrosis. Re-programmed AECIIs play a key role in the pathogenesis of pulmonary fibrosis, producing TGF-? and pro-inflammatory mediators leading to activation of lung fibroblasts and recruitment of macrophages that further deregulate repair. Our long-term goal is to dissect transcriptional regulation of pulmonary fibrosis. We recently identified a novel pro-fibrotic regulator, Foxm1, a member of the family of Forkhead Box (Fox) transcription factors. Our preliminary data demonstrated that Foxm1 is induced in AECII within fibrotic lesions, but not in normal alveolar region of human and mouse lungs, indicating that Foxm1 can be a marker of re-programmed AECIIs. Transgenic expression of activated Foxm1 transcript in mouse AECII exacerbated radiation-induced pneumonitis and caused severe pulmonary fibrosis. Conditional deletion of Foxm1 from AECII attenuated radiation-induced lung fibrosis. While these data demonstrate that AECII promote pulmonary fibrosis through Foxm1-mediated events, the downstream signaling pathways regulated by Foxm1 in AECII remain to be identified (objective). We will test hypothesis that reprogrammed hyperplastic AECII promote pulmonary fibrosis through Foxm1-mediated activation of fibroblasts and recruitment of myeloid inflammatory cells into fibrotic lesions. By combining genetic and pharmacological approaches in radiation- and bleomycin-induced mouse models of lung fibrosis, the proposed studies will identify molecular mechanisms regulated by Foxm1 in AECII, and determine contribution of hyperplastic Foxm1-positive AECII to ling fibrogenesis. In Aim 1, we will determine the role of Foxm1-positive AECII in activation of fibroblasts. Using transgenic mice with Foxm1 gain-of-function and loss-of-function, and single cell RNA-seq analysis of AECII isolated from human IPF lungs, we will identify Foxm1 target genes. Since our preliminary data show increased expression of pro-fibrotic and inflammatory mediators in Foxm1-overexpressing AECII, we will examine whether Foxm1 activates transcription of Osteopontin and TGF?1 genes in AECII, and stimulates activation of latent TGF?1 protein, causing activation of lung fibroblasts. In Aim 2, we will examine whether Foxm1 activates CCL2 and CXCL5 genes in AECII, leading to recruitment of myeloid inflammatory cells into fibrotic lungs. In Aim 3, we will use novel small molecule Foxm1 inhibitor recently discovered in my laboratory to inhibit AECII re-programming, lung inflammation and fibrotic remodeling in murine models of pulmonary fibrosis. Completion of our studies will (1) identify novel molecular mechanisms whereby Foxm1 induces pulmonary fibrosis, and (2) test efficacy of novel Foxm1 inhibitors in lung fibrosis.